AN ELASTIC BASE GRINDING WHEEL FOR SMOOTHING AND POLISHING TOROIDAL CONTOURS OF HARD MATERIALS

Abstract: The elastic base grinding-wheel for the smoothing and polishing of toroidal contours of hard materials comprises a rigid-material support body, which may also be divided into two parts (1A, 1B) along an equatorial plane in a substantially centered position, has an internal shape (2, 3) suitable for mating operatively with the motor shaft with which it is coupled, and an external (4) shape congruent with that of the contour of the material to be smoothed and/or polished. At least a wing (5, 6) at one and/or the other end of the support body (1), is arranged for receiving and holding a coating (12) of elastomeric material injected or vulcanized in situ. The part (13) of the injected coating (12) of elastomeric material directed towards the workpiece is coated with elements (14) of relatively flexible abrasive material, so that the overall contour corresponds to the final shape that must have the workpiece after the smoothing and/or polishing.

Description: An elastic base grinding wheel for smoothing and polishing toroidal contours of hard materials — ooo — The present invention relates to an elastic-base grinding wheel for smoothing and polishing toroidal contours of hard materials. In the art of working of hard materials, and in particular of marble finishing and polishing, grinding wheels are used to operate on the previously worked part. The known grinding wheels are generally made of magnesite, resinous materials or the like, and in any case, they are made of rigid materials and, as a consequence, serious problems are encountered owing to variations of the thickness of marble slabs, granite or stone to be machined because since the grinding wheels known in the art are rigid, they cannot correctly match and adhere and consequently operate on the whole surface of the various contours encountered. Also, grinding wheels made out of a vulcanized rubber body are known, provided with cemented diamond-coated cloth suitable for smoothing and polishing, but this kind of construction shows both the problem of an excessive cost of the vulcanized rubber body and the problem of having a non uniform compliance since the areas where the rubber thickness is smaller, owing to their excessive flexibility, do not adhere adequately to the contour to be machined. In practice, in grinding operation and subsequent finishing operations up to polishing or honing of rigid and hard materials such as glass, marble, granite and the like, two kinds of techniques have been developed. The first kind entails the use of very rigid shaped bodies for grinding, finishing and polishing. The machining bodies having high rigidity are mainly utilized in extreme precision operations such as optical pieces or high-precision mechanical parts. The working operations with rigid bodies, even if they provide excellent results insofar as the dimensional tolerances are concerned, are however very slow: the optical polishing for e.g. large dimensions telescope mirrors may last for months or even years. The second kind entails the use of either flexible or deformable shaping bodies made of felt, rubber or the like. The flexible bodies do not allow a precise working, but however allow to perform the working in extremely short times. These short working times are bound to the skill of the operator and show difficulties in working shaped bodies such as those having a toroidal contour. As a matter of fact in working a hard material that can be polished, abrasives having a decreasing grain size are used with the progress of the finishing operations. When grinding and polishing bodies are used, which incorporate the abrasive materials, if the shaping bodies are either flexible or elastic, it is difficult to obtain a correct matching in the subsequent passes with grinding bodies including abrasives having a decreasing grain size. The aim of the present invention is to provide a smoothing and polishing tool for hard materials in particular with toroidal shapes or the like that allows to combine the advantages of the two techniques above mentioned allowing to perform precision working characteristic of rigid shaping bodies and the speed of operation typical of elastic or flexible shaping bodies. According to the present invention, the grinding wheel comprises a rigid material supporting body, having an internal shaping arranged for operational coupling with a motor-driven spindle on which it is mounted, and an external part having a shape matching the contour of the materials to be smoothed and/or polished. One or more wings, provided either at one or both the ends of the body of the grinding wheel, are arranged for accommodating and holding a coating of an elastomeric material locally injected or vulcanized. The part of the injected elastomeric coating directed toward the material being worked is coated with portions of relatively flexible abrasive material, so that the overall contour corresponds to the final shape that must reach the material being worked after the smoothing and/or polishing. According to a first embodiment, the supporting body is realized with a single piece part. According to a further embodiment, the supporting body is comprised of two emisymmetrical parts with respect to a center-line, between which, at the moment of the assembly thereof, and before the elastomeric coating has been injected, can possibly be inserted spacers for modifying the final contour of the grinding wheel in order to satisfy different operational requirements. In this last embodiment, there results the advantage consisting in the fact that the single parts that will constitute the support body may be realised without undercuts, allowing to obtain the single pieces by injection moulding of thermoplastic material with low-cost moulds, as it will be clear to a person skilled the art. The present invention will be now disclosed with reference to embodiments thereof presently preferred, referred to only as a non limiting example, and according to the figures of the attached drawings wherein: Figure 1 shows a first embodiment of the grinding wheel according to the invention, partially broken and partially cut away; Figure 2 shows a second embodiment of the grinding wheel according to the invention, partially cut-away and partially broken; Figure 3 shows a sectional view along a diameter of the grinding wheel shown in Figure 2; and Figure 4 shows a modification of the structure shown in Figure 3. It is stressed that the shaping of the part performing the abrading action, as represented in the figures, is given only as a non limiting example, because the present invention is directed to the structure of the grinding wheel, independently from the specific contour herein disclosed referred to for ease of discussion. With reference to Figure 1, the grinding wheel comprises a body 1 of a rigid material such as aluminium, PVC, or the like, having an internal shaping generally shown in 2 and 3, arranged for mating in a known way will a motor driven spindle with means not shown. The body 1, on its external part, has a contoured part 4, matching the contour to be worked and a pair of wings 5 and 6. It is to be remarked that with some contours to be machined only one of the wings 5 or 6 may be provided The wings 5 and 6 have circumferential channels 7, 8 and holes 9, 10, distributed along the channels 7, 8. The holes 9 and 10 are arranged in a corresponding way to be radiused with grooves 11 in the contoured part 4. As it can more clearly seen in the left part of the figure, on the body 1 there is realised a coating 12 of an elastomeric material, preferably locally injected or vulcanized, having a hardness Shore B between 50 and 70, and preferably between 58 and 64. The channels 7 and 8, the holes 9 and 10, as well as the grooves 11 have the purpose of holding firmly the coating 12 of elastomeric material also in the presence of the very high stresses due both to the centrifugal force and to the torque. It is remarked that normally these kinds of grinding wheels run at a speed of about 6000 r.p.m. On the part 13 of the coating 12 facing the work piece there are fastened, preferably by thermal welding, strip shaped abrasive elements 14, having a certain flexibility, of a kind known in the art. The operation techniques of the above disclosed grinding wheel are known to a person skilled in the art and therefore will not be discussed into detail. It is to be noted that the structure of the grinding wheel according to the invention is such so as to limit an excessive expansion of the elastomeric element caused by the centrifugal force that would lead to a modification of the intended contour. Moreover, the body of the grinding wheel is such to accommodate the entire surface of the contour of the workpiece, that had been shaped in advance. It is stressed again that the particular shaping of the working contour that has been shown is referred to only as a non limiting example and that such contour, jointly will the shaping of the rigid body 1 and the number of " wings 5 and 6, may change according to specific requirements, while retaining the technical teaching of the locking structure of the coating of elastomeric material. With reference to Figure 2, there is shown a grinding wheel similar to that of Figure 1, with the difference that the center body is divided along its equator in two separate parts that are however coupled together and shown in 1A and IB. Such arrangement may be better seen in Figure 3. With this construction, the body parts 1A and IB may be realized in thermoplastic material, such as Nylon, with simple injection moulding techniques since the bodies 1A and IB do not have undercuts that would render complex and costly the moulds. If it is desired that the bodies 1A and IB be made of metal, these could be easily produced by die-casting of aluminium alloys or the equivalent and the dies may be of simple construction. In Figure 3 there is shown a modification of what has been illustrated in Figures 2 and 3. Between the bodies 1A and IB there are inserted spacers 20, 21, of annular shape that are embedded into the injected body 12' of elastomeric material. In this way different shapes of the external contour of the injected body 12' may be obtained in order to satisfy different requirements in the operation of the grinding wheel. In Figure 4, the spacers 20, 21 are shown as annular rings with a cylindrical wall, with a circumference that corresponds to the throat part of the bodies 1A and IB. Clearly this is a simplification, but it is naturally conceivable that the spacers may assume different shapes for realizing different contours of the injected body 12'. By means of the splitting of the bodies 1A and IB, and the possible use of the spacers 20, 21, one can realise grinding wheels with different contours of the injected body 12' for different kinds of working operations, reducing the number of base components, reducing consequently the inventory costs and also the production costs. The body 1, 1A, IB of the grinding wheel is preferably realized in thermoplastic materials known under the name Kemiton, commercially available from FRAMPLAST S.p.A., moulded with an injection moulding machine, or with other thermoplastic materials, such as Franprene, Neoprene, Santoprene, all commercially available from MONSA1 O S.p.A. The hardness may range between 65 and 75 Shore, according to the diameter of the grinding wheel to be moulded. For instance for grinding wheels having a diameter of 110/120 millimetres, it is preferable to use a hardness of 65 Shore; for a diameter of 130 millimetres a hardness of 70 Shore is preferable, and for diameters of 140/160 millimetres a hardness of 75 shore is preferable. As a matter of fact, with the increase of the diameter, the peripheral speed increases and consequently the centrifugal force increases, compromising the mechanical strength. Therefore, this problem has been solved by increasing the hardness concurrently with the increase of the grinding wheel diameter. Now the technique for fastening the strip abrasive elements shown in 14 and constituted of diamond-coated, commercially available from SORMA, cloth, will be disclosed. From test that have been performed, it has been found that the diamond- coated cloth members cannot be simply glued because they would not withstand the stresses caused by the centrifugal force and the impacts with the stone, particularly in difficult areas, such as corners and the like. Consequently it has been necessary to rely on chemical welding, and it has been found convenient a chemical welding performed with the product commercially known as Loctite 401, commercially available from LOCTITE ITALIA, i.e. an adhesive of the class of cyanoacrylates. The process consists in cutting the cloth in strips not wider than 6-7 millimetres in order to allow the matching with the coating 12 of the grinding wheel; to apply a small quantity of the Lactate, commercially available from LOCTITE ITALIA, adhesive on the cloth, to press the cloth onto the coating 12 for a few moments up to the complete bonding of the two bodies. A final step, having a great importance, is the filling of the exposed areas 13 between the cloth strips, as well as the filling of all the spaces between each abrasive dot in the diamond coated side of the cloth. Such coating has two purposes of paramount importance: 1) to eliminate the danger of "hook-up" to the corners of the material being worked; 2) to avoid smears or streaks, i.e. the small grooves that would derive from the dot pattern of the abrasive. Between the dots there are empty spaces in bands that cause such smears or streaks in the material being worked. Such filling is performed with a cement HARD-PVC, commercially available from VULLJN BISON MASTIC, with added a percentage from 20 to 30% of tin oxide, and from 4 to 8% of diamond powder. In this way a use duration ranging from 3 to 5 times more with respect to the systems used on the market may be assured.

Claims: Claims 1. An elastic base grinding- wheel for the smoothing and polishing of toroidal contours of hard materials, characterized in that it comprises a rigid-material support body (1), having an internal shape (2, 3) suitable for mating operatively with the motor shaft with which it is coupled, and having an external (4) shape congruent with that of the contour of the material to be smoothed and/or polished; at least a wing (5, 6) at one and/or the other end of the support body (1), arranged for receiving and holding a coating (12) of elastomeric material injected or vulcanized in situ: the part (13) of the injected elastomeric coating (12) directed towards the workpiece being coated with elements (14) of relatively flexible abrasive material, so that the overall contour corresponds to the final shape that must have the workpiece after the smoothing and/or polishing. 2. A grinding wheel according to claim 1, characterized in that the at least one wing (5, 6) is provided with a circumferential channel (7, 8); and with a plurality of holes (9, 10) distributed along said circumferential channel (7, 8), the holes being coupled to grooves (11) arranged in the external part of the support body (1) for receiving the coating (12) of elastomeric material. 3. A grinding wheel according to claim 2, characterized in that the circumferential channels (7, 8), the holes (9, 10) and the grooves (11) cooperate for stably securing the coating (12) of elastomeric material of the support body (1) and for limiting the elastic deformations caused by the centrifugal force and the operation stresses during the use of the grinding wheel. 4. A grinding wheel according to any of the preceding claims characterized in that the external part (13) of the coating (12) of elastomeric material directed towards the workpiece is coated with elements (14) of abrasive material for smoothing and/or polishing. 5. A grinding wheel according to one or more of the preceding claims characterized in that the body (1) is divided along an equatorial plane in a position substantially centered between the wings (5, 6), the division being arranged so that the two body parts (1A, IB) do not have undercuts. 6. A grinding wheel according to claim 5, characterized in that the parts constituting the support body (1) are obtained by light-metal die-casting. 7. A grinding wheel according to claim 5, characterized in that the parts constituting the support body (1) are realized with injection-moulded thermoplastic resin. 8. A grinding wheel according to claim 7, characterized in that the thermoplastic resin is Nylon. 9. A grinding wheel according to one or more of claims 5 to 8, characterized in that in correspondence with the division on an equatorial plane of the body, there are arranged one or more spacer elements (20, 21). 10. A grinding wheel according to claim 9, characterized that said one or more spacer elements (20, 21) on the equatorial plane are realized and shaped to constitute an adapter base for the coating of elastomeric material in order to realize an external contour of the grinding wheel congruent with the contour of the material being worked. 11. A grinding wheel according to any of the preceding claims, characterized in that the external part (13) of the coating (12) of elastomeric material directed towards the workpiece is coated with elements (14) of abrasive material for smoothing and/or polishing. 12. A grinding wheel according to claim 11, characterized in that the coating with abrasive material is constituted of relatively flexible strip elements (14) provided externally with an abrasive layer. 13. A grinding wheel according to claim 11, characterized in that the abrasive material is distributed as dots. 14. A grinding wheel according to claim 13, characterized in that the spaces between the dots of abrasive material and the spaces between the strip elements (14) are covered with a paste of a binding agent and powdered abrasive material. 15. A grinding wheel according to one or more of the preceding claims, characterized in that the strip elements (14) are fastened to said coating (12) of elastomeric material by chemical bonding. 16. A grinding wheel according to claim 15, characterized in that the chemical bonding is realized by means of a cyanoacrylate adhesive. 17. A grinding wheel according to any of the preceding claims, characterized in that the coating (12) of elastomeric material has an hardness between 65 and 75 Shore B. 18. A grinding wheel according to any of the preceding claims, characterized in that the coating (12) of elastomeric material is constituted of Kemiton, commercially available from FRAMPLAST S.p.A., or Franprene or Neoprene or Santoprene, all commercially available from MONSANTO S.p.A.

Inventors: LUPI QUINTILIO, LUPI, QUINTILIO
Applicants: LUPI QUINTILIO, LUPI, QUINTILIO
Application year: 1994
Main classification: B24D13
IPC codes: B24D5, B24D9, B24D13, B24D18